Abstract : Commercial arbitration is a private mechanism intended to settle disputes between two or more parties who have agreed to it beforehand by means of an arbitration clause. However, in practice, one notes that arbitrators often deviate from the doctrinal rule governing the relative effect of contracts in order to render the arbitration process more effective. This occurs frequently in arbitration proceedings involving companies. The aim of this article is to illustrate how arbitrators may utilize various means in order to involve non-signatory companies in the process. Generally, arbitrators view as a tacit consent to the arbitration proceedings participation in the constitution of an arbitration tribunal. Moreover, if by its conduct, a non-signatory company becomes confused with a signatory to the agreement, arbitrators often extend the effects of the arbitration agreement when this confusion may be harmful to the interests of third parties or when it is contrary to public order. Finally, when certain conditions are met, the abuse of rights doctrine as well as the «group enterprise theory» may be effective means for arbitrators to include in the arbitration proceedings, either by constraint or voluntarily, a party who has not signed the arbitration agreement.